Petri dishes have been used for cell culture for many years. They are generally circular transparent glass or plastic dishes having a substantially flat bottom and a relatively low (in relation to the diameter of the dish) side wall. Glass and most plastics are, however, non-conducting and generally it is not possible to subject cells growing in a Petri dish to an electric field of any significant intensity. It is known that most cells, when subjected to an electric field undergo changes in their cell wall structure with the formation of holes through which a foreign gene, in the form of DNA or RNA, or other non-permeant molecule such as protein nucleotides or drugs, may be inserted, in a process which is known as electroporation.
For the introduction of DNA, electroporation has mostly been used for cells which cannot be easily transfected by the classical Graham and Van der Eb (1973) calcium technique, such as lymphocytes and bone marrow stem cells, which do not adhere to solid supports. Consequently, current electroporation techniques call for cells to be in suspension in a medium containing the DNA when the electric field is applied. Attention is directed to Canadian Patent 1,208,146 dated Jul. 22, 1986 to Wong. Attention has now turned, however, to the use and study of cells which do adhere to a solid substrate and which only grow when so adhering. Attempts to produce a suspension of such cells using a proteolytic enzyme, such as trypsin, substantially alters the cell membrane, the main barrier to DNA entry, and interferes with cell viability and reproducobility.